1. Field of the Invention
The present invention relates to a method of making an electric circuit device which is formed by connecting electric circuit components through an electrical bonding member.
2. Related Background Art
The following methods are known as methods for electrically connecting electrical circuit components:
(1) Wire Bonding Method
(2) TAB (Tape Automated Bonding) Method (as disclosed in, for example, Japanese Patent Unexamined Publication No. 59-139636)
(3) CCB (Controlled Collapse Bonding) Method (as disclosed, for example, in Japanese Patent Examined Publication No. 42-2096 and Japanese Patent Unexamined Publication No. 60-57944)
(4) The method as shown in FIGS. 1 and 2
(5) The method as shown in FIG. 3
(6) Method as Shown in FIG. 4
The method (4) as shown in FIGS. 1 and 2 will be described.
An insulating film 71 made of polyimide or the like material is formed on a portion of a first semiconductor device 4 other than a connecting portion 5, while a metallic member 70 such as Au is provided on the connecting portion 5. Subsequently, the semiconductor has exposed surfaces 73, 72 of the metallic member 70 and the insulating film 71. On the other hand, an insulating film 71' of polyimide or the like material is formed on the portion of a second semiconductor device 4' other than the connecting portion 5'. At the same time, a metallic member 70' such as Au is provided on the connecting portion 5'. Then, after smoothing the exposed surfaces 73' and 72' of the metallic member 70' and the insulating film 71', the first and second semiconductor devices 4 and 4' are located as shown in FIG. 2, followed by a thermal press-connecting so that the connecting portions 5 and 5' of the first and second semiconductor devices 5 and 5' are electrically connected to each other through the metallic members 70 and 70'.
The method (5) shown in FIG. 3 is as follows.
This method employs an anisotropic conductive film 78 which is formed by dispersing conductive particles 79 in a conductive material 77 and disposed between a first circuit board 75 and a second circuit board 75'. After locating the first and second circuit boards 75 and 75', these circuit boards are bonded at their connecting portions 76 and 76' by application of pressure with or without simultaneous application of heat.
The method (6) shown in FIG. 4 is as follows.
This method employs an elastic connector 83 which is composed of metal wires 82 such as Fe and Cu embedded in an insulating material 81 and which is provided between first and second circuit boards 75 and 75'. After locating the first and second circuit boards 75 and 75', pressure is applied so that the connecting portions 76 and 76' of the first and second circuit boards 75 and 75' are connected to each other.
The above-described connecting methods, however, suffer from the following problems:
(a) Restrictions in the circuit design due to connecting
(b) Too large a pitch of conductors, i.e., too large a distance between the centers of the adjacent conductors
(c) Difficulty in reducing thickness of the device
(d) Low reliability due to corrosion or breakage of conductors, as well as degradation of the characteristics due to concentration of thermal stress in the region of connecting between the connecting member and the electrical circuit component
(e) Difficulty when a defective electrical circuit component is to be replace.
The method shown in FIGS. 1 and 2 has encountered the following problems:
(a) The number of steps is increased and the cost is raised due to necessity for smoothing the exposed surfaces 72 and 73 of the insulating film 71 and the metallic member 70 or the exposed surfaces 71' and 70' of the insulating film 71' and the metallic member 70'.
(b) The quality of the electrical connection between the metallic member 70 and the metallic member 70' is impaired when there is any unevenness of the exposed surfaces 72, 73 of the insulating film 71 and the metallic member 70 or when there is any unevenness of the exposed surfaces 72', 73' of the insulating film 71' and the metallic member 70'.
The method as shown in FIG. 3 encounters with the following problems.
(a) Generally, it is difficult to apply the connecting pressure uniformly to the connecting portion 76, 76' after locating the circuit boards 75 and 75'. This causes a fluctuation in the state of connecting, with the result that the contact resistance in the bonded region fluctuates wildly. In consequence, the reliability of the bond is undesirably impaired. In addition, this connecting method is not suitable for use in the cases where a large electrical current flows, because the supply of large electric current causes significant heat generation in the bonded region.
(b) Fluctuation of the resistance value is unavoidable even if the pressure can be applied uniformly, due to the arrangement of conductive particles 79 in the anisotropic conductive film 78, with the result that the reliability of the bond is impaired. In addition, this method is not suitable for use in the case where the product device is supplied with a large electrical current.
(c) It is difficult to attain a high density of connections because a reduction in the pitch of the connecting portions, i.e., distance between the centers of the connected regions, reduces the resistance between the adjacent connecting portions.
(d) It is necessary that the projected amount h.sub.1 of connecting portions 76, 76' from the circuit boards 75, 75' has to be controlled precisely because the resistance value undesirably fluctuates depending on the projected amount h.sub.1.
(e) When an anisotropic conductive film is used for the connection between a semiconductor device and a circuit board or between first and second semiconductor devices, it is necessary to form bumps at the connections to the semiconductor devices. In consequence, this causes a disadvantage that the production cost is raised in addition to the above-mentioned problems (a) to (d).
Furthermore, the following problems (a) to (d) are caused when the art shown in FIG. 4 is applied to the connection between a semiconductor device and a circuit board or between first and second semiconductor devices.
(a) It is necessary to employ a specific pressing jig in order to apply the connecting pressure.
(b) The reliability of connection is impaired due to fluctuation in the contact resistance between the metal wire 82 of the elastic connector 83 and the connecting portion 76 of the first circuit board 75 or the connecting portion 76' of the second circuit board 75'.
(c) Since the metallic wires 82 in the elastic connector is basically rigid, there is a risk that the elastic connector 83, the first circuit board 75 and the second circuit board 75' could be broken if too large a connecting pressure is applied thereto. Conversely, a connecting that is too small tends to impair the reliability of the connection.
(d) A fluctuation in the resistance value and the breakage of the circuit boards 75, 75' and the elastic connector 83 tend to be caused by fluctuations in the projected amount h.sub.2 of the connecting portions 76, 76' of the circuit boards 75, 75' and the projected amount h.sub.3 of the metallic wires 82 of the elastic connector 83.
It is therefore necessary that suitable measures be taken to minimize the fluctuation in the projected amounts.